DE102018218449A1 - Protection against accidental contact for radio interference suppressed voltage transformers in a potential-free DC voltage network - Google Patents

Abstract

Voltage converter (1) for converting between a DC voltage at a DC voltage gate (2) and a single or multi-phase AC voltage at an AC voltage gate (3) by timing an electronic switching device (4), via which each phase (3a-3c) of the AC voltage gate ( 3) can optionally be connected to the positive pole or to the negative pole of the DC voltage gate (2), the positive pole and / or the negative pole of the DC voltage gate (2) being connected to a ground connection (7) via at least one capacitor (5, 5a, 5b) is connected, the ground connection (7) being connectable to an external ground (7a) and the connection between the capacitor (5, 5a, 5b) and the ground connection (7) being made via at least one switching element (6, 6a, 6b) Electric drive train (10) for a motor vehicle (100). Motor vehicle (100) with the electrical drive train (10).

Description

The present invention relates to voltage converters which can be used, for example, in electrically driven vehicles and which are radio interference suppressed with one or more capacitors.

State of the art

Electric motors in the drive train of electrically powered vehicles are generally fed with a multi-phase AC voltage. The electrical energy is usually provided on board the vehicle by batteries, fuel cells or other energy sources as DC voltage. The multi-phase AC voltage is generated from this DC voltage with an inverter. For this purpose, the phases of the AC voltage supply for the electric motor are alternately connected to the positive pole and the negative pole of the DC voltage source in rapid time intervals. This is implemented via an arrangement of switching elements in the inverter.

Due to the timing, the AC voltage is subjected to high-frequency interference, which does not hinder the operation of the electric motor, but is coupled into metallic structures of the vehicle via the connection of the electric motor to the vehicle mass. The metallic structures can then act like transmitting antennas and radiate the interference into the environment, which is not compatible with the requirements for electromagnetic compatibility (EMC). One way of suppressing the interference is to connect the DC voltage supply feeding the inverter to the vehicle ground via so-called Y capacitors.

Since the intermediate circuit voltage is typically several hundred volts and is therefore dangerous for people when touched, there are regulatory requirements regarding the maximum amount of energy that can be capacitively stored in the DC voltage network. The EP 2 763 868 B1 also suggests that the DC link capacitors be discharged in a controlled manner during certain events, particularly in the event of an accident.

Disclosure of the invention

In the context of the invention, a voltage converter for converting between a DC voltage at a DC voltage gate and a single-phase or multi-phase AC voltage at an AC voltage gate was developed. The conversion takes place by timing an electronic switching mechanism, via which each phase of the AC voltage gate can be connected either to the positive pole or to the negative pole of the DC voltage gate. The positive pole and / or the negative pole of the DC voltage gate is connected to a ground connection via at least one capacitor, which in turn can be connected to an external ground, such as a vehicle ground of an electrically driven vehicle. The connection between the capacitor and the ground connection is made via at least one switching element.

It was recognized that especially when using the voltage converter in a vehicle, the risk potential of the energy stored in the capacitor is drastically reduced if the capacitor is separated from the vehicle ground by the switching element.

If one pole of the capacitor is connected to the vehicle ground, the potential-free nature of the DC voltage network is eliminated. A person standing at ground potential therefore only has to touch the pole of the DC voltage network to which the capacitor is connected in order to close the circuit and receive an electric shock. If both poles of the DC voltage gate (and thus of the DC voltage network) are each connected to the vehicle ground via a capacitor, it does not matter which of these poles is touched.

If, on the other hand, the connection between the capacitor and the vehicle ground is disconnected, a pole of the capacitor is no longer accessible to a person who operates the vehicle normally and, for example, works on a charging connection to charge the traction battery. Only those who could unauthorizedly open the housing of the voltage transformer, ignoring the warnings that the device still contains stored energy after disconnection from the vehicle's DC network, could come into contact with both poles of the capacitor.

Thus, the capacitor that is switched off in this way falls completely out of the balance of the energy which may be dangerous for humans. This is particularly advantageous in situations in which the vehicle is connected to a charging station, because at this moment energy is also stored in the charging cables and in the charging station itself, and the overall hazard, i.e. stored energy in the vehicle, cables and charging station.

At first glance, it may seem absurd to deprive a capacitor of all functions, which serves an important purpose such as radio interference suppression. The inventors have recognized that those impressed from the voltage converter on the AC voltage gate Interference is only emitted when the electric motor is active and the interference can therefore reach the vehicle ground. However, this is also the state in which the vehicle is in motion and cannot be touched by people outside the vehicle. However, if the vehicle is stationary and can be touched, the electric motor is not active and the effect of the interference suppression capacitors is not required.

Unlike when discharging the capacitor, there is no conflict of objectives between a high insulation resistance on the one hand and a low discharge resistance on the other hand when switching off with the switching element, and the switching off works independently of the capacitance of the capacitor. The previous safety-related limitation of the capacity is therefore completely eliminated. So there is no longer a conflict of aims between good interference suppression, for which a high capacity is advantageous, and personal protection, for which a low capacity is better. Capacitors with a larger, previously not permissible capacitance can be used. In addition to the better interference suppression effect, these capacitors sometimes have clear advantages in terms of the required installation space in comparison to the toroidal capacitors with lower capacitance used to date.

Thus, in an advantageous embodiment, the capacitor has a capacitance of at least 500 nF, preferably of at least 1 μF and very particularly preferably of at least 10 μF. The specific capacity to be selected is given by the frequency to be filtered.

In a further particularly advantageous embodiment, the voltage converter is designed to use the switching element to interrupt the connection between the capacitor and the ground connection when an acceleration or deceleration force acting on the voltage converter exceeds a predetermined threshold value. Such an acceleration or deceleration force can act, for example, in an accident. After an accident, it is particularly important to make the vehicle safe to touch so that rescue workers are not endangered during the rescue work.

For example, the voltage converter can be coupled to an acceleration sensor and, in response to the fact that a high acceleration has been registered, actuate the switching element. However, the switching element itself can also be designed, for example, to interrupt the connection of the capacitor to the ground connection at high acceleration forces. For this purpose, a predetermined breaking point can be provided, for example, which is destroyed when the force is applied. The connection is inevitably interrupted even if the vehicle's control units or microcontrollers are no longer functional.

In a further particularly advantageous embodiment, the voltage converter is designed to use the switching element to establish the connection between the capacitor and the ground connection when a consumer connected to the AC voltage gate of the voltage converter is activated, and to disconnect the connection again when the consumer is deactivated. As described above, radio interference is only emitted when the voltage converter is used in a vehicle, for example, when the motor supplied with the voltage converter is active. If the engine is not active, the vehicle is at a standstill. By now disconnecting the connection to the ground connection in this state, maximum contact security is provided whenever the vehicle can in principle be touched by people outside the vehicle.

In principle, any reversible electrical switch is suitable for reversible switching, for example an electromechanical relay. Higher reliability and wear resistance, especially with very frequent switching operations, can be achieved with semiconductor switches. Therefore, in a further particularly advantageous embodiment, the switching element comprises an arrangement of at least two transistors, the transistors comprising bipolar transistors and / or field-effect transistors, and those defined by the respective collector-emitter path or by the respective source-drain path Forward directions of the transistors are connected in antiseries to one another. The antiserial circuit is required because a collector-emitter path, or a source-drain path, can only block voltages of one polarity and the polarity with which the capacitor is charged is not known from the outset.

In a further particularly advantageous embodiment, the connection between the capacitor and the ground connection is made via a series circuit comprising a plurality of switching elements. If one switching element is inoperable and can no longer interrupt the connection, the other switching element can take over this function. Personal protection is thus still guaranteed, so that in the event of a switch malfunctioning, for example, it is still permissible to charge a vehicle with the voltage converter at a charging station.

If the connection between the capacitor and the ground connection could no longer be interrupted and the maximum permissible capacity would be exceeded when connecting to a charging station, the charging function of the vehicle would have to be deactivated Be blocked for security reasons. The range of the vehicle would then be limited by the current energy supply.

If, on the other hand, a switch fails so that the connection of the capacitor to the ground connection can no longer be established, this is not immediately dangerous for people, but only the radio interference suppression by the capacitor becomes ineffective. This condition should also be remedied promptly, but it is not so critical that the onward journey must be stopped immediately and an expensive breakdown service must be used.

In a further particularly advantageous embodiment, diagnostic means are provided which are designed to detect the correct function and / or the actual switching state of at least one switching element. On the one hand, due to the safety-relevant function of the switching element, a regulatory obligation can arise to make the switching element diagnosable. On the other hand, the state in which the connection between the capacitor and the ground connection is permanently interrupted is undesirable with regard to electromagnetic compatibility (EMC). Especially when using the voltage converter in a vehicle, the vehicle without effective radio interference suppression becomes a source of broadband radio interference that is difficult to locate because it is only sporadically active and at the same time mobile. Since these faults do not have a direct impact on the driving behavior of the vehicle, the malfunction for the driver without diagnosis means initially remains unnoticed until the Federal Network Agency has determined the vehicle as the source of the fault and corresponding follow-up costs are incurred.

In a further particularly advantageous embodiment, at least one switching element is designed as a switch between a first switching position and a second switching position. The switching element connects the ground connection, or a further switching element connected between this switching element and the ground connection, in the first switching position to a voltage source for a test potential and in the second switching position to the capacitor. The diagnostic means comprise means for monitoring the test potential. A test program can then be run, for example when the voltage converter is started up and / or recurrently during operation, in which combinations of the switching positions of existing switching elements are set and measurements of the test potentials are compared with the values to be expected.

Alternatively or also in combination, in a further particularly advantageous embodiment the diagnostic means comprise a voltage source which is connected to the side of at least one switching element facing away from the ground connection, and means for monitoring the potential on this side of the switching element. This configuration does not presuppose that the switching element is a changeover switch, but also works with switching elements that can only either connect or disconnect the connection between the capacitor and the ground connection, such as the arrangements of transistors described above.

As described above, an essential application of the voltage converter is to supply an electric motor in an electrically driven vehicle. Therefore, the invention also relates to an electric drive train for a motor vehicle with the voltage converter described and an electric motor connected to the AC voltage gate of the voltage converter.

Furthermore, the invention also relates to a motor vehicle with this drive train, the electric motor and the ground connection of the voltage converter being connected to a common ground of the motor vehicle. In this way, the interference injected from the voltage converter into the electric motor and from there into the mass of the motor vehicle

The current path from the point at which the electric motor is connected to the ground of the motor vehicle to the point at which the ground connection of the voltage converter is connected to the ground of the motor vehicle should cover the smallest possible area. In this way, the length of the antenna effective for the emission of interference, and thus the efficiency for this radiation, is significantly reduced.

In a further advantageous embodiment, the motor vehicle comprises a rechargeable battery for feeding the drive train and a safety device which is designed, in response to a determination by diagnostic means of the voltage converter, that due to a malfunction of one or more switching elements, the connection between the capacitor and the The ground connection of the voltage converter cannot be interrupted to prevent the battery from being charged from an energy source external to the vehicle. In this way, situations in which the total capacitively stored energy exceeds a critical value due to the connection of the vehicle-external energy source are advantageously avoided. At the same time, the driver is forced to repair, since the vehicle can only be used in the potentially unsafe condition if the energy currently available in the battery is sufficient.

In a further advantageous embodiment, the motor vehicle comprises a safety device which is designed, in response to a determination by diagnostic means of the voltage converter, that the connection between the capacitor and the ground connection of the voltage converter cannot be established due to a malfunction of one or more switching elements, to issue a warning to the driver and to prevent the motor vehicle from being started up again after a predetermined driving distance or time, and / or to limit the speed and / or torque of the electric motor. As described above, a constantly interrupted connection is not acutely dangerous, but it means that the vehicle no longer meets the requirements with regard to electromagnetic compatibility (EMC). Since the fulfillment of these requirements is a prerequisite for the approval of the vehicle and the driver is generally responsible for the technically perfect condition of his vehicle, it is appropriate to force the driver to repair even in this fault situation.

Further measures improving the invention are described in more detail below together with the description of the preferred exemplary embodiments of the invention with reference to figures.

Figure list

• 1 Beispielhafte schematische Darstellung eines Spannungswandlers 1 in einem Antriebsstrang 10, der in einem Kraftfahrzeug 100 verbaut ist;
• 2 Beispielhafte schematische Detailansicht von Schaltelementen 6a, 6b, die als Umschalter ausgebildet sind, und zugehörigen Diagnosemitteln 8;
• 3 Beispielhafte schematische Detailansicht transistorierter Schaltelemente 6a, 6b und zugehöriger Diagnosemittel 8.

It shows:

• 1 Exemplary schematic representation of a voltage converter 1 in a drivetrain 10th in a motor vehicle 100 is installed;
• 2nd Exemplary schematic detailed view of switching elements 6a , 6b , which are designed as change-over switches, and associated diagnostic means 8th ;
• 3rd Exemplary schematic detailed view of transistorized switching elements 6a , 6b and associated diagnostic tools 8th .

To 1 serves the voltage converter 1 in the drive train 10th of the motor vehicle 100 to it, one at its DC gate 2nd convert the applied DC voltage into a three-phase AC voltage on the three phases 3a , 3b , 3c its AC voltage gate 3rd is issued. With this AC voltage, the electric motor 11 in the drive train 10th fed. The conversion takes place by timing an electronic switching mechanism 4th , which is not shown in further detail.

Due to the timing in the rear derailleur 4th the AC voltage is subjected to high-frequency interference. Because the electric motor 11 at the point 101 with the crowd 110 of the motor vehicle 100 is connected, these disturbances couple into metallic parts of the motor vehicle 100 . These metallic parts act as antennas that radiate the high-frequency interference. Hence the pole T + of the DC voltage gate 2nd over the capacitor 5a with the ground connection 7 of the voltage converter 1 connected. The pole T- of the DC voltage gate 2nd is about the capacitor 5b with the ground connection 7 of the voltage converter 1 connected. These connections are through the switching element 6 guided. The ground connection 7 is on point 102 with the crowd 110 of the motor vehicle 100 as an external mass 7a connected.

Inside the powertrain 10th can also be combined several capacities on a common ground potential, which in turn with the ground 110 of the motor vehicle 100 connected is. This is particularly easy in the motor vehicle, for example 100 can be installed if the drive train 10th is a closed assembly that is integrated into the motor vehicle as a whole 100 is integrated.

If the switching element 6 is switched to continuity, the high-frequency interference from the vehicle mass 110 back to the voltage converter 1 pulled and short-circuited. In this way, the radiation of these disturbances into the environment is significantly reduced. However, the vehicle mass is in this state 110 with one pole of each of the two capacitors 5a , 5b connected. When handling the vehicle 100 then just touching one of the two poles is enough T + , T- of the DC voltage gate 2nd to get an electric shock from in one of the capacitors 5a , 5b to get stored energy.

Therefore, it is advantageous if the electric motor 11 is not active and radio interference suppression by the capacitors 5a and 5b the switching element is not required 6 switched to interruption. The one with the switching element 6 connected pole of each of the two capacitors 5a , 5b is then no longer accessible to people, so the capacitance of these capacitors 5a , 5b no longer represent a potential hazard.

This is especially important if the traction battery 120 of the motor vehicle 120 from an external charging station 200 charging because the charging station 200 and the cable connection to the motor vehicle 100 bring in additional capacities.

Diagnostic devices are used to monitor this safety-relevant function 8th intended. Two types of malfunctions can occur.

On the one hand, the switching element 6 stuck in the switch position for continuity, which has the consequence that the connection between the capacitors 5a , 5b and the ground connection 7 can no longer be interrupted. Especially when charging the traction battery 120 from the charging station 200 there would be a risk of electric shock. Therefore, in this case, by the safety device 130 prevents charging. The driver of the vehicle 100 must with that in the battery 120 remaining energy reserves and go to a workshop.

On the other hand, the switching element 6 stuck in the switch position for an interruption. In this case the vehicle is 100 always safe to touch, but there is no radio interference suppression. Therefore, in this case, by the safety device 135 issued a warning to the driver. If the error is not remedied within a specified route or time, the vehicle is started up again 100 prevented. So there is also an obligation to repair this error. Instead of restarting the vehicle 100 To completely prevent it, only the speed and / or the torque of the electric motor 11 be restricted to the vehicle 100 can at least reach a workshop under their own steam ("limphome function").

In order to reduce the likelihood that charging must be stopped due to an error, the in 2nd Embodiment shown two switching elements 6a and 6b connected in series. The switching elements 6a , 6b are designed here as relays.

The switching element 6a connects in its in 2nd switch position shown the second switching element 6b with the voltage source 81a for a test potential. In its in 2nd Switch position, not shown, connects the switching element 6a the second switching element 6b with the capacitors 5a and 5b .

The switching element 6b connects in its in 2nd Switch position shown the ground connection 7 with the voltage source 81b for a test potential. In its in 2nd Switch position, not shown, connects the switching element 6b the ground connection 7 with the capacitors 5a and 5b , this connection still through the switching element 6a is conveyed.

The diagnostic tools 8th include in addition to the voltage sources 81a and 81b additional funds for the test potential 82a , 82b to monitor these test potentials, which in this example are implemented as analog-digital converters with series resistors. Each of the four combinations of switching states of the switching elements 6a and 6b nominally leads to a unique combination of voltage values by the analog-to-digital converter 82a , 82b be registered. In this way, the actual switching states of the switching elements 6a and 6b be determined.

In the in 3rd The exemplary embodiment shown is also a series connection of two switching elements 6a , 6b between the capacitors 5a , 5b and the ground connection 7 intended. In contrast to 2nd are the switching elements 6a , 6b however, each implemented as an anti-serial circuit of two MOSFET transistors. Such switching elements do not act like the relays in 2nd , as a switch, but can only, according to the representation of the switching element 6 in 1 , be switched to either continuity or interruption. Hence the diagnostic tools 8th organized differently here. On the the ground connection 7 opposite side of each of the switching elements 6a , 6b feeds a voltage source 83a , 83b test voltage via a series resistor. About means 84a , 84b the potential is monitored there. In this way it can be determined whether between the means 84a , 84b and the ground connection 7 there is passage.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 2763868 B1 [0004]

Claims (13)

Voltage converter (1) for converting between a DC voltage at a DC voltage gate (2) and a single-phase or multi-phase AC voltage at an AC voltage gate (3) by timing an electronic switching mechanism (4) via which each phase (3a-3c) of the AC voltage gate ( 3) can optionally be connected to the positive pole or to the negative pole of the DC voltage gate (2), the positive pole and / or the negative pole of the DC voltage gate (2) having at least one capacitor (5, 5a, 5b) with a ground connection (7) is connected, the ground connection (7) being connectable to an external ground (7a) and the connection between the capacitor (5, 5a, 5b) and the ground connection (7) being made via at least one switching element (6, 6a, 6b) is. Voltage converter (1) after Claim 1 , The voltage converter (1) is designed to use the switching element (6, 6a, 6b) to interrupt the connection between the capacitor (5, 5a, 5b) and the ground connection (7) when the voltage converter (1) is connected Acceleration or deceleration force acts that exceeds a predetermined threshold. Voltage converter (1) after Claim 1 , wherein the voltage converter (1) is designed to establish the connection between the capacitor (5, 5a, 5b) and the ground connection (7) with the switching element (6, 6a, 6b) when connected to the AC voltage gate (3) of the Voltage converter (1) connected consumer is activated, and to disconnect again when the consumer is deactivated. Voltage converter (1) according to one of the Claims 1 to 3rd , wherein the switching element (6, 6a, 6b) comprises an arrangement of at least two transistors, the transistors comprising bipolar transistors and / or field effect transistors and wherein the through the respective collector-emitter path or through the respective source-drain path , defined forward directions of the transistors are connected to one another in an anti-serial manner. Voltage converter (1) according to one of the Claims 1 to 4th The connection between the capacitor (5, 5a, 5b) and the ground connection (7) is made via a series connection of several switching elements (6a, 6b). Voltage converter (1) according to one of the Claims 1 to 5 Diagnostic means (8) are provided which are designed to detect the correct function and / or the actual switching state of at least one switching element (6, 6a, 6b). Voltage converter (1) after Claim 6 , wherein at least one switching element (6, 6a, 6b) is designed as a changeover switch between a first switching position and a second switching position, the switching element (6, 6a, 6b) being the ground connection (7), or one between this switching element (6, 6a , 6b) and the ground connection (7) connected further switching element (6, 6a, 6b), in the first switching position with a voltage source (81a, 81b) for a test potential and in the second switching position with the capacitor (5, 5a, 5b) connects and wherein the diagnostic means (8) comprise means (82a, 82b) for monitoring the test potential. Voltage converter (1) according to one of the Claims 6 to 7 The diagnostic means (8) have a voltage source (83a, 83b) which is connected to the side of the at least one switching element (6, 6a, 6b) facing away from the ground connection (7), and means (84a, 84b) for monitoring the potential this side of the switching element (6, 6a, 6b). Voltage converter (1) according to one of the Claims 1 to 8th , wherein the capacitor (5, 5a, 5b) has a capacitance of at least 500 nF, preferably of at least 1 µF and very particularly preferably of at least 10 µF. Electrical drive train (10) for a motor vehicle (100), comprising a voltage converter (1) according to one of the Claims 1 to 9 and an electric motor (11) connected to the AC voltage gate (3) of the voltage converter (1). Motor vehicle (100) with an electric drive train (10) according to one of the Claims 1 to 10th The electric motor (11) and the ground connection (7) of the voltage converter (1) are connected to a common ground (110) of the motor vehicle (100). Motor vehicle (100) after Claim 11 , further comprising a rechargeable battery (120) for feeding the drive train (10) and a safety device (130) which is designed in response to a determination by diagnostic means (8) of the voltage converter (1) that due to a malfunction of a or more switching elements (6, 6a, 6b) the connection between the capacitor (5, 5a, 5b) and the ground connection (7) of the voltage converter (1) cannot be interrupted to prevent charging of the battery (120) from an energy source (200) external to the vehicle. Motor vehicle (100) after Claim 11 , further comprising a safety device (135) which is designed, in response to a determination by diagnostic means (8) of the voltage converter (1), that due to a malfunction of one or more switching elements (6, 6a, 6b) the connection between the Capacitor (5, 5a, 5b) and the ground connection (7) of the voltage converter (1) cannot be produced, issue a warning to the driver and prevent the motor vehicle (100) from being started up again after a predetermined route or time, and / or restrict the speed and / or the torque of the electric motor (11).

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